Technical Field
The present disclosure relates to methods and nanocomposites for the removal of aromatic hydrocarbons from contaminated water sources and systems. More particularly, the present disclosure relates to a nanocomposite containing metal oxide nanoparticle impregnated carbon nanotubes, a process for producing the nanocomposite and methods of treating contaminated water sources with the nanocomposite to adsorb and remove aromatic hydrocarbons.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Benzene, toluene, ethyl benzene and xylene (collectively referred to as BTEX) are established aromatic hydrocarbon contaminants of water sources. These compounds are classified as flammable, toxic, carcinogenic and/or mutagenic [W. J. Deutsch and R. Siegel, Groundwater Geochemistry: Fundamentals and Applications to Contamination. CRC Press, 1997, p. 232; and C. Kent, Basics of Toxicology, vol. 13. John Wiley & Sons, 1998, p. 194.—each incorporated herein by reference in its entirety]. Thus, their presence in aqueous solution is a significant environmental concern, even at low concentrations. The health effects these pollutants cause in humans include disturbance of the kidney, liver and blood systems, skin and sensory irritation, respiratory problems, cancer, leukemia, and central nervous system depression. As a result of these health concerns, the U.S. EPA has set a maximum contaminant level of 5 μg/L for benzene in drinking water and the U.S. Public Health Service has recommended no more than 2 mg/L of toluene in water for lifetime exposure.
These compounds are widely used in several chemical production and manufacturing processes including petroleum refiners, as well as the polymer, plastic and paint industries as solvent, a natural fraction of petroleum and as precursors for the manufacturing of different chemicals. Water draining from these industries is highly contaminated with BTEX and the pollutants must be removed before water is discharged from any of these industrial facilities [J. A. Kent, Kent and Riegel's Handbook of Industrial Chemistry and Biotechnology: Vol. 1. Springer Science & Business Media, 2010, p. 391; and John J. McKetta Jr, Encyclopedia of Chemical Processing and Design: Volume 67—Water and Wastewater Treatment: Protective Coating Systems to Zeolite. CRC Press, 1999, p. 289.—each incorporated herein by reference in its entirety]. Further, the pollutants are frequently found in groundwater due to inadvertent spills during production and/or transportation, leaks in underground storage tanks and pipelines, leaching from landfills and improper waste disposal practices. These pollutants migrate easily in the water system, with little or no tendency of being confined near the origin of contamination.
There have been many studies aimed at the removal of aromatic hydrocarbons such as benzene from water. The reported remediation methods include wet air oxidation [B. A. Abussaud, N. Ulkem, D. Berk, and G. J. Kubes, “Wet Air Oxidation of Benzene,” Ind. Eng. Chem. Res., vol. 47, no. 514, pp. 4325-4331, 2008.—incorporated herein by reference in its entirety], photo catalytic degradation [M. Bahmani, V. Bitarafhaghighi, K. Badr, P. Keshavarz, and D. Mowla, “The photocatalytic degradation and kinetic analysis of BTEX components in polluted wastewater by UV/H2O2-based advanced oxidation,” Desalin. Water Treat., vol. 52, no. 16-18, pp. 3054-3062, May 2013; and M. N. Chong, B. Jin, C. W. K. Chow, and C. Saint, “Recent developments in photocatalytic water treatment technology: a review,” Water Res., vol. 44, no. 10, pp. 2997-3027, May 2010.—each incorporated herein by reference in its entirety], and adsorption using various materials [I. Ali and V. K. Gupta, “Advances in water treatment by adsorption technology,” Nat. Protoc., vol. 1, no. 6, pp. 2661-7, January 2006.—incorporated herein by reference in its entirety]. However, each technique is characterized by its inherent limitations, which create the continuous need for improvements in methods for the removal of aromatic hydrocarbons such as BTEX from contaminated water sources.
Adsorption has become one of the most promising and increasingly practiced industrial techniques for removing aromatic hydrocarbons such as benzene from water using such varied absorbents as sand, peat and activated carbon [Y. Kalmykova, N. Moona, A.-M. Strömvall, and K. Björklund, “Sorption and degradation of petroleum hydrocarbons, polycyclic aromatic hydrocarbons, alkylphenols, bisphenol A and phthalates in landfill leachate using sand, activated carbon and peat filters,” Water Res., vol. 56, no. 0, pp. 246-57, June 2014; and N. Wibowo, L. Setyadhi, D. Wibowo, J. Setiawan, and S. Ismadji, “Adsorption of benzene and toluene from aqueous solutions onto activated carbon and its acid and heat treated forms: influence of surface chemistry on adsorption,” J. Hazard. Mater., vol. 146, no. 1-2, pp. 237-42, July 2007; and C. L. Mangun, Z. Yue, J. Economy, S. Maloney, P. Kemme, and D. Cropek, “Adsorption of Organic Contaminants from Water Using Tailored ACFs,” no. June 1996, pp. 2356-2360, 2001.—each incorporated herein by reference in its entirety].
Carbon nanotubes (CNTs) have attracted great interest as adsorbents because of their unique chemical structure and intriguing electrical, mechanical and physical properties facilitating the adsorption of different chemicals including organic, inorganic and biological materials [W. Chen, L. Duan, and D. Zhu, “Adsorption of Polar and Nonpolar Organic Chemicals to Carbon Nanotubes,” Environ. Sci. Technol., vol. 41, no. 24, pp. 8295-8300, December 2007; and V. K. Gupta, S. Agarwal, and T. a Saleh, “Chromium removal by combining the magnetic properties of iron oxide with adsorption properties of carbon nanotubes,” Water Res., vol. 45, no. 6, pp. 2207-12, March 2011.—each incorporated herein by reference in its entirety]. These carbon nanotubes have high surface areas, are easily modified on their surface to aid adsorption, and are especially well-suited to waste water treatment [O. G. Apul and T. Karanfil, “Adsorption of Synthetic Organic Contaminants by Carbon Nanotubes: A Critical Review,” Water Res., vol. 68, pp. 34-55, October 2014; and X. Qu, P. J. J. Alvarez, and Q. Li, “Applications of nanotechnology in water and wastewater treatment,” Water Res., vol. 47, no. 12, pp. 3931-3946, August 2013; and X. Liu, M. Wang, S. Zhang, and B. Pan, “Application potential of carbon nanotubes in water treatment: A review,” J. Environ. Sci., vol. 25, no. 7, pp. 1263-1280, July 2013.—each incorporated herein by reference in its entirety].
Despite many studies indicating that CNTs have a high affinity for adsorbing organic chemicals and the potential for developing carbon nanotubes for BTEX water treatment and removal [C.-J. M. Chin, M.-W. Shih, and H.-J. Tsai, “Adsorption of nonpolar benzene derivatives on single-walled carbon nanotubes,” Appl. Surf. Sci., vol. 256, no. 20, pp. 6035-6039, August 2010; and F. Tournus and J.-C. Charlier, “Ab initio study of benzene adsorption on carbon nanotubes,” Phys. Rev. B, vol. 71, no. 16, p. 165421, April 2005; and Y. Liu, J. Zhang, X. Chen, J. Zheng, G. Wang, and G. Liang, “Insights into the adsorption of simple benzene derivatives on carbon nanotubes,” RSC Adv., vol. 4, no. 101, pp. 58036-58046, October 2014—each incorporated herein by reference in its entirety] there remains many possibilities for developing different types of carbon nanotubes with different morphologies [S. Iijima, “Helical microtubules of graphitic carbon,” Nature, vol. 354, no. 6348, pp. 56-58, 1991.—incorporated herein by reference in its entirety] and functionalization for enhancing their affinity for specific contaminants and improving their removal efficiencies as adsorbents.
Surface modification of carbon nanotubes to enhance BTEX adsorption from aqueous solutions has proven effective. For example, Su et al. employed multi-walled carbon nanotubes (MWCNTs) that were oxidized by sodium hypochlorite (NaOCl) solution to enhance the adsorption of benzene and toluene from aqueous solution [F. Su, C. Lu, and S. Hu, “Adsorption of benzene, toluene, ethylbenzene and p-xylene by NaOCl-oxidized carbon nanotubes,” Colloids Surfaces A Physicochem. Eng. Asp., vol. 353, no. 1, pp. 83-91, January 2010.—incorporated herein by reference in its entirety]. NaOCl-oxidized CNTs have superior adsorption performance compared with many types of carbon and silica adsorbents previously reported in the literature. The work has been extended to additional aromatic hydrocarbons including xylene and ethyl benzene [F. Yu, J. Ma, and Y. Wu, “Adsorption of toluene, ethylbenzene and xylene isomers on multi-walled carbon nanotubes oxidized by different concentration of NaOCl,” Front. Environ. Sci. Eng. China, vol. 6, no. 3, pp. 320-329, June 2011.—incorporated herein by reference in its entirety].
In view of the foregoing, it will be advantageous to design methods, composites and processes for economically producing those composites that can efficiently and at a low cost treat aromatic hydrocarbon contaminated water. One object of the present disclosure is to provide a metal oxide nanoparticle impregnated carbon nanotube nanocomposite for adsorptive removal of these pollutants.